Control for internal-combustion engines and their variable pitch propellers



May 25, 1954 J. M. EAsTMAN ET AL 2,679,297

CONTROL FOR INTERNAL-OONBUSTION ENGINES AND THEIR VARIABLE PITCHPROPELLERS Filed July 29, 1946 6 Sheets-Sheet l May 25, 1954 J. M.EASTMAN ET AL 2,679,297

CONTROL FOR INTERNAL-coMBUsTloN ENGINES AND THEIR VARIABLE FITCHPROPELLERS Filed July 29, 194e 6 Sheets-Sheet 2 T0 WATER /M- .jYTE/Vdj'p' 5500? missy/76216 o Tlll] 4 TTOIP/VEY May 25, 1954 J. M. EASTMANET AL 2,679,297

CONTROL FOR INTERNAL-coMusTroN,ENGINES AND THEIR VARIABLE PITcHPROPELLERS Filed July 29, 1946 6 Sheets-Sheet 3 \z x l N Q N Q May 25,1954 J. M. EAsTMAN ET AL 2,679,297

CONTROL FOR INTERNAL-COMBUSTION ENGINES AND THEIR VARIABLE FITCHPROPELLERS Filed July 29, 1946 6 Sheets-Sheet 4 '//7' 12/ l a Y 'T-'4 7,arrai/vff May 25, 1954 J. M. EASTMAN ET AL 2,679,297

CONTROL FOR INTERNAL-OOMBUSTION ENGINES ANO THEIR VARIABLE FITCHPROPELLERS Flled July 29, 1946 6,Sheets-Sheet 5 www Mao? Arme/vf? U @Y\E\\\\\ N www EN k 0 O RMN mf, x w SON Y www l! May 25, 1954 J. M.EAs'rMAN ET AL 2,679,297

coNTRoL FoR INTERNAL-COMBUSTION ENGINES AND THEIR VARIABLE FITCHPRoPELLERs Eiled'JuIy 29, 194e e sheets-sheet e FEE Patented May 25,1954 UNITED STAT CNTRL FR INTERNAL-COMBUSTION ENGINES AND THEIR VARIABLEPITCH PRPELLERS James lid. Eastman, Edwin G. Keller, and Frank C. Mock,South Bend, Ind., assigner-s to Bendix Aviation Corporation, South Bend,ind., a corporation of Delaware Application July 29, 1946, Serial No.686,942

53 Claims. 1

This invention relates to controls for internal combustion engines, andparticularly to boost and power controls for automatically maintaining agiven power output at varying altitudes as determined by the setting ofa power control lever or like control device.

An object of the invention is to provide an improved power control unitfor use with an engine having a variable capacity supercharging systememploying uid pressure means for varying the ratio ofengine-to-supercharger speed;

Another object is to provide improved power control mechanism for anengine having a variable-capacity supercharging system employing one ormore fluid couplings for varying the enn gine-to-supercharger speedratio which will maintain manifold pressure at a substantially constantvalue for a given setting of a power control lever or analogous memberthrough auto matic regulation of an air throttle or device having anequivalent function up to a point where charging capacity is approachedor attained for wide-open throttle, and to thereafter maintain the setcharging pressure by automatically controlling the admission of iiuidpressure to said couplings;

ther objects include the following:

To provide an automatic power control unit of the variable datum typeadapted for use with an engine having a throttle-controlled inductionpassage and a variable capacity supercharging system utilizing one ormore duid couplings for varying the ratio of engine-to-superchargerspeed, incorporating an improved hydraulic control system which amongother advantages requires a minimum of manual effort by a pilot oroperator;

To provide a power control unit of the variable datum type for an enginehaving a variable capacity supercharging system including one or morefluid couplings for var the ratio of engine-to-supercharger speed,wherein the datum mechanism acts automatically to not only adjust thethrottle position up to charging capacity for wide-open throttle butalso acts to shift the control irom 4lie throttle to a fluid meteringdevice for metering iiuid under pressure to said coupling' or couplings;

l To provide an hydraulically operated power 4control unit wherein apilot may regulate the charging pressure and power output eitherautomatically or manually, and in case of failure of the automaticcontrol, the pilot will have immediete manual control; 'To provide anautomatic power control unit (Cl. Nil-135.74)

wherein the pilot will have manual control available in a selected rangeof manifold pressures, as for example, during the taxying range ofthrottle opening;

To automatically correlate manifold pressure and engine speed throughthe medium of a single power control lever with a minimum of manualeffort;

To provide in a variable datum automatic power control unit improvedmeans for manually overriding the datum setting in the cruise range;

To provide improved means in an hydraulic type of power control unit forstabilizing the operation of the control;

To provide in a power control unit means whereby different take-offsettings may be had for engines having different characteristics;

To provide in an hydraulic type of power control unit means forcirculating a relatively large quantity of fluid through the unit forwarming up purposes, and for automatically returning the circulation ofhuid to normal at any time desired after the warming up operation;

To provide means for conveniently overriding the upper limit of manifoldpressure for introduction of an anti-detonating fluid such as water;

To provide means whereby the manifold pressure will follow apredetermined curve for a given power setting up to some given altitudeor condition of air density as determined by thediiferental betweenscoop pressure and engine intake or manifold pressure and willthereafter droop or be held to a value such that heating due to a highrise across the supercharger will not produce detonaticn; and

To generally improve power controls, particularly those of the hydraulictype.

The foregoing and other objects and advantages will becorne apparent inview of the following description taken in conjunction with thedrawings, wherein:

Figure l is a view in elevation of an aircraft engine having the powercontrol unit of the present invention operatively connected thereto;

Figure 2 is a schematic diagram of the power control unit with theengine and supercharger drive system omitted;

Figures 3 and 4 are sectional views of portions of Figure 2 enlarged tomore clearly show the parts;

Figure 5 is a schematic diagram of the pro peller pitch or engine speedcontrol unit;

Figure 5 is an enlarged section of the metering valve for the fluidcouplings;

Figure '7 is a detail fragmentary view of part Si of an adjustment forthe engine speed 01 propeller pitch control unit;

Figure 8 is a schematic diagram of a variable speed drive adaptable toan engine having a single stage supercharging system;

Figure 9 is a schematic diagram of the power control unit of Figure 2but showing a modified form of damping system; and

Figure 10 is a curve chart illustrating the action of the altitude dreopmechanism.

Referring to the drawings, and first to Figure 1, an aircraft engine isindicated at ill having an air induction conduit l i, li' which receivesair from an air scoop or like device, part of which is indicated at i2.For the purposes of illustration, the air induction or input system isof the multistage type, including a supercharger I3 herein termed themain stage, which is engine-driven with a fixed gear ratio and suppliespressure under all conditions of operation, and a supercharger I4 hereintermed the auxiliary stage since it is regulated to supplement thesupercharger I3 under certain conditions of operation, as at wide openthrottle when the capacity of the main stage supercharger is reached. Acharge forming device such as a carburetor is shown at l5 including aventuri l5', and posterior the carburetor is a throttle valve i6 forvariably limiting the supply of air flowing to the intake manifold il ofthe engine and inders. While the throttle i5 is shown positionedposterior to the carburetor and anterior the supercharger i3, it may belocated at any desired point in the induction system. A stop i6 limitsthe wide-open position of the throttle. The engine is equipped with apropeller i3, preferably of the variable pitch type, the pitch of theblades being adjustable through the medium of a governor i9 controlledby a lever 23. Since devices of this type have long been known and usedfor controlling` the speed of aircraft engines and may be purchased as acomplete unit in the open market, it is not shown in detail in thepresent instance, it being sufficient to state that the position oflevel` 28 determines the setting of the governor and hence engine speedat a given setting of the power control device, movement of the lever2li to the left decreasing the pitch of the propeller blades-andincreasing engine speed for a given position of a power control leverhereinafter decribed and movement of said lever 2D to the rightincreasing the pitch and decreasing engine speed for a given position ofsaid power control lever.

A pressure type oil supply system includes an oil tank 2l from which oilis taken by a pump 22 and delivered under pressure to the engine throughconduit 23, scavenged oil being returned to the tank :2i through returnline 24 and cooler 25. The engine may be vented to the top of the oiltank through line 2t.

The drive on the auxiliary stage supercharger is transmitted from theengine or other suitable power source through variable speed hydrauliccoupling units generally indicated at 2l' and 2l', which may be ofsimilar construction and have similar operating characteristics.Hydraulic couplings of this type are well known in the art and may bepurchased in the open market. In genera-l, each unit consists of adriving rotor or impeller 28 and a driven rotor or vaned runner 29mounted in a casing Eli, oil under pressure being conducted to the unitthrough conduitSi. The rotor 23 is usually driven from a suitable thenceto the respective engine cylq power source through step-up or step-downtransmission; in the present instance it is shown secured on a shaft 32driven from the engine through gearing 33. rlhe drive transmitted to theunit lll is oi a ratio higher than that of the unit El so that he twounits will cover a range of speed sufficient to give the necessaryauxiliary charging capacity. The rotor or vaned runner 29 drives a shaftSli carrying a gear 35. Corresponding parts of the coupling unit 2l havebeen given corresponding reference numerals except that a prime has beenadded. The gears 35, 35 and 3S, 3E iorrn part of a transmission systemfor driving the supercharger i4.

Oil under pressure fed to the rotors through conduits 3 i, 3 i' reducesthe slip between the driving rotors 2S, 28 and the driven rotors orrunners 2t, 2t', the amount of slip being in relation to the rate offeed of the oil. With little or no oil pressure, the rotors or runners2e, 29' simply idle or produce very little additional load on thesystem. A certain amount of oil thrown outwardly through bleeds formedin the rotors is returned to the drain system through conduit 3l. Theconduit 3l to the low speed coupling is controlled by a valve 36operating to close the said conduit Vwhen the driven shaft tri rotatesfaster than the driving shaft 32. rIhis action causes the low speedcoupling to automatically empty when the high speed coupling attains apredetermined speed and overdrives the low speed coupling, to therebyavoid loss of power which would otherwise be absorbed by the rotatingoil-filled low speed coupling. rhe valve is shown schematically, sinceit forms no part of the present invention and may be obtained as a.complete unit in the open market.

Power control unit The various parts which go to make up the powercontrol unit are mounted in a main casing or housing il and are shownschematically to avoid a multiplicity of sectional views. Basically, thedevice provides for control of manifold pressure by automatic and/ormanual regulation of the carburetor throttle up to some predeterminedaltitude or condition of air density, usually termed the rst criticaland requiring a wideopen throttle, and beyond this point, the manifoldpressure is controlled by automatic regulation of the hydrauliccouplings; the carburetor throttle control and hydraulic couplingcontrols being interconnected and correlated, preferably through acommon aneroid and variable datum assembly. in addition, the unit mayselectively incorporate additional controls and provisions for meetingthe requirements of engines having different operating characteristicsas well as special requirements of different engine manufacturers, animportant advantage of the improved power control unit being itsflexihility in this respect. To facilitate an understanding of theinvention, the description been broken down with respect to the severalcontrols and their method of operation.

Control through regulation of the carburetor throttle A main shaft il(Figures 2 and 4) is journaled in the housing i0 and has secured thereonexteric-rly of the housing the one extremity of a lever said lever beingprovided with an extension s2 projecting upwardly at a slight angle tosaid lever and carrying a stub shaft H2 rotatably mounting a piniongear43. The lower or opposite end of level l2 is pivotally connected tothecarburetor t .rottle by linkage 44, 44. A main power control lever isindicated at 15; it connects through linl de with a lever 55 pivotallymounted on il i, also externally or" the casing lit, and at its upp rextremity beyond said shaft the lever red and is provided with alaterally l toothed segment [l and a cam It?, wl' liter may beconsidered the speed control cam ince it may be used to select enginespeed according to a predetermined power setting of the main powercontrol lever. The toothed segment :i5 meshes with the pinion i3 carriedby the extension ft2 of the throttle lever 42, and said pinion in turnis in mesh with one set oi teeth t8 of a segmental gear t3, loosely orpivotally mounted on the main sha-ft il and provide-i with another setof teeth l in with a toothed rack lil secured on a piston rod E@ shownas of I-beam shape in cross-section, said rod 5l! terminating at itsopposite ends in pistons El, 5l slidable in cylinders :'52 and 53. Inthe cylinder 5i is a spring 5d which at one end ts the piston 5l andnormally urges it and consequently the rack te toward the extreme lefthand position (closed throttle position), and at its opposite endengages in a recess formed in the rear end wall of the cylinder 52.

The rack te is actuated by huid under pressure admitted. to thecylinders 52 and 53 by a servo valve (see Figure 3) whose position isdetermined by a variable datum manifold pressure assembly including anevacuated bellows or aneroid 53 mounted in a sealed chamber 5l dened inpart by a cup-shaped wall and in part by a diaphragm 5i) whose centralportion is clamped between a pair of reinforcing plates connected to acup-shaped guide member 6E! having an encircling bushing at one endmounted for limited sliding movement in a cylinder El and at itsopposite end provided with a ball head slidingly mounted in a guide boreor passage :E2 which is provided with a Vent E2' to facilitateevacuation of the bellows, after which the vent may be closed by a screwor other suitable means and the vent sealed. The bellows may beevacuated to a low absolute value and rendered responsive to changes inpressure only, or iu may be evacuated and loaded with a temperatureresponsive inert gas and a clamping fluid to render the bellowsresponsive to changes in both temperatures andpressure; see U. S. patentto Mock et No. 2,376,711 for a suitable density responsive capsule ofthe latter type.

The datum of the bellows is determined by variably loading a datumspring G3 which at one end abuts a piston es slidingly mounted in acylinder S5 and at its opposite end abuts a thrust plate ce forming partof a thrust bearing carried by an abutment or contact plate t? securedon the one extremity of a datum rod or shaft et, the opposite end ofsaid rod or shaft having connected thereto a balkheaded bolt t3 whichengages in a socket at the adjacent end of the guide E6 and provides auniversal joint connection between the datum rod te and the movable end.of the bellows 55. A sealing diaphragm 5S seals the space around theaneroid shaft 53. A datum cam l@ (Figures 2 and ll) is formed on theupper ared extremity of the lever 4E so as to be rotatable throughadjustinent of said lever, the cam 'lil being engaged by a follower l!mounted on the one arm of 'l2' oi a lever l2, the latter also having anoppositely projecting arm l2" mounting a cam follower 'it' adapted toengage cams lll and |38 under certain conditions and for a pur'' pose tobe described. Lever l2 is pivoted on a pin 15 projecting laterally froma stationary depending bracket l5. A lever l1 is pivotally mounted orfulcrumed at 'i8 to the follower lever 'I2 so as to be movabletherewith. A compression spring 'F3 normally urges the follower lever112 in a clockwise direction, tending to maintain the follower 7lagainst the cam lil. A link 8S is pivotally connected at one end to thelower end of lever 'll and at its opposite end is pivoted on a pin 8l(Figure 3) which is carried by a swinging arm 82 and also serves as afloating pivot or fulcrum for a servo lever 83 whose upper end isoperatively connected to a servo valve St, designed to control admissionof luid under pressure in baci: of the piston E@ in a manner to bedescribed. The lower end of lever 83 is contoured to engage the pistontill, being held against it by the action of servo valve spring 84'; andthe relative dimensions of said lever and the partsA which make up thefloating pivot 3l therefor are such that the travel or" pivot iii actsto move servo valve t in a direction to cause oil pressure change inback of piston @il to move said piston and lever 83 and return servovalve 24 to the position shown, thereby setting the load on spring 63 inaccordance with the travel of pivot 8l to determine the datum setting.Utilizing a servomotor to tension the datum spring relieves the pilot ofconsiderable manual effort to eiect this operation.

A servo lever 85 is pivoted or fulcrunied at S6 to a stationary bracket,and at its upper end said lever is engaged by contact plate 5l and atits lower end engages and actuates servo valve 55 to the left againstthe tension of springs Si', S7 mounted in a cylinder 88 and having adamping piston E8 interposed therebetween.

The various operating pressures in the flow ducts, servo valve ports,servo piston cylinders and like chambers and passages have beendesignated as follows:

P-l-engine manifold air pressure P-Z-engine oil pressure P--drain oilpressure P-ll-throttleopening piston pressure Pe-throttle-closing pistonpressure P--coupling valve piston pressure P--metered oil to lowcoupling P-$-feed oil to low coupling P-9rnetered oil to high couplingP-l-feed oil to high coupling E43-feedback damping piston pressure P-ll-aneroid chamber pressure P-i -datum piston pressure P-l-propellerspeed increasing piston pressure P-l-propeller speed decreasing pistonpresure P-lil`atmospheric or scoop pressure The high pressure liuid(P-Z) is indicated by inpointing arrows where it enters the unit fromthe engine oil system to the servo valve 55. This valve may beconsidered the main servo valve, since it controls the flow of highpressure fluid to the throttle pistons Si, 5l', and also to the couplingvalve piston lili to be described. From valve 55, the flow may bereadily traced by fol.- lowing the various channels designated as aboveindicated. High pressure oil also branches orf from the 13 2 entrancechannel before the latter reaches the valve 55 for initiating certainoperations which will subsequently be described.

Operation of th'rottleqcontrol At sea level, with the throttle nearlyclosed and the engine idling, the parts will occupy substantially'thepositions shown'in the drawings. At this'time, cam follower 1i is inengagement with the low portion of cam i and the oating pivot 8| is inthe neighborhood of its left-hand positiongor in a position such thatthe datum spring G3 is loaded with but a moderate force which isinsufficient to prevent partial-collapse of bellows 56, even though themanifold pressure is relatively low during idling. Also, at this timethe servo valve 55 will be in a positionsuch that the oil pressure P-fiin piston chamber 53 isat a minimum and pressure P-t in piston chamber52 plus spring be will have moved pistons 5I, 5l to the left-handposition, thus substantially locking the gear tz'against rotation.

If the power control lever 45 -is now moved a limited distance to theright, gear 4G will be rotated counterclockwise, rolling pinion 43 in. asimilar direction and turning throttle lever-42 counterclockwise,thereby opening the throttle l5. Throughout a certain predetermined lowpower range of control, the servo valve will be in a position such thatpiston chamber 53 will `be open to drain and piston chamber 52 open toP-Z pressure, forcing throttle pistons 5I, 5I to their extreme left-handpositions, this being the range of direct manual control. Should' lever45 be moved to the right to :a position such that the cam 'lil (actingthrough lever l2, link 30, iloating pivot 8i and servo valve Sil),increases the load on the datum spring 63 to a point such that thespring force overcomes the pressure tending to hold the bellows 5Scollapsed, datum rod t8 will move to the right and move servo valve 55to the left to a point where high pressure luid P-'2 will'pass'tochamber 53 and oil will drain from chamber 52. Throttle pistons 5 l, 5lwill now move to the right, and acting through rack' 69 and gear 48,will roll pinion i3 counterclockwise on'gear 46 and open the throttlele. The control .now becomes automatic, or the boost control takes over,the pilot selecting the degree of manifold pressure by positioning camit whichinlturn' .locates the floating pivot 8i. Ii while in theautomatic range of control, the pilot moves lever Z55 in apowerincreasing direction, pivot Si is repositioned to the right andservo-lever 33 is also moved to the right, permittineA servo-springt? tomove servo valve Btl to the right so that high pressure fluid P-2 willpass to P-i, moving piston E4 to the right and compressing datum spring63. vShould this force be sufficient to overcome kthe pressure tendingto hold bellows 55 collapsed, datum rod G8 moves to the right and actingthrough servolever 85 moves servo valve 55 from its equilibrium positionto the leit. High pressure fluid then flows from P-2 te P-i and Yfluidis also drained from P- to P-, and pistons 5! 5l move to the right andopen the throttle to a point where the increased manifold pressurebalances the datum spring load or datum setting.

To reduce power output while in the automatic range of control, lever ismoved to the left, cam 'iii permits compression spring 'F9 to repositionfloating pivot 8i to the left and lever 83 'then moves servo valve froma neutral or equilibrium position to the left and opens P-l to drain.

Piston and datum rodf now move to the left and servo valve to the right.'High pressure oil then flows from 124-2 to P-5 and oil is drained fromP4-4to P-t, whereupon pistons'y 5i, 5I :move to thellle'ft and racklllactsy through: segmental gear 43 and pinion t3 to move throtle lever 42in a direction'to close the throttle l5 and reduce manifold pressureuntil the pressure on the right oi diaphragm 59 and in chamber 5lbalances the new datum setting.

Should there be a decrease in air density, as by a gain in altitude,pressure P-i at the righthand side of diaphragm 59 and the pressure P-I4in chamber il will likewise decrease, and the aneroid will tend toexpand or extend itself, thereby moving datum shaft Se to the right,turning servo valvelever clocswise and` moving servo vaive 55 to theleft. High pressure oil then flows trol i P- to P-l. and oil is alsobled from P- to IJ-3, and pistons 5l, 5i move to the right, turingsegmental gear 'd counterclockwise and rolling pinion lf3 to the left,thereby moving throttle lever i2 to the-right or in a direction to openthe throttle and increase the manifold pressure until the pressure onthe right of diaphragm 5s and in chamber 5l balances the datum settingof the spring $3.

Should there be an increase in air density as by a drop in altitude,pressure P-l at the right of diaphragm 5s and pressure P-ll in chamber5l will likewise increase, bellows will tend to collapse, therebypermitting datum spring E3 to move datum shaft 58 to the left, whereuponservo valve 55 will move to the right due to pressure of springs-8l.8l'. Pressure oil then ows from P- to 'i3-5, and oil is drained from P-to P-3, whereupon pistons 5i, 5i' move to the left, rack l-acts throughsegmental gear d?, to roll pinion 43 to the right, thereby movingthrottle lever ri to the left er in a direction to close the throttlevalve ES and reduce manifold pressure until P-l on the right sioe ofdiaphragm 59 balances the datum setting of spring S3.

Should oil pressure, either intentionally through manipulation of valve89, to be described, or through leakage or o'her causes, be shut oilfrom the-unit or the oil channels which conduct operating pressure tothe pistons 5i, 5 i spring 55. will move said pistons to the left-handposition thereo, the closed throttle position. Manual control for thefull stroke of lever to" is then attainable, whic.. may range fromclosed-up to a throttleopening position iimited only by the throw of thepilots lever Q5 and/or the elective travelof the inter-engagingdifferential gearing 43, 56, 4 8. n actual practice, manual control hasbeen found desirable from a fully closed-up to approximately one-halfthrottle opening.

When pistons 5l and 5l are in their throttleclosing position to theleft, should the lever 45 and the cam It be set to call for a manifoldpressure which is below that which said pistons will .allow when thisposition, the latter will be pushing aga-inst a stop in an effort tofurther close the throttle. However, since the pistons cannot move anyfurth r toward the left, the actual throttle position will be determinedsolely by the leverI fio acting on pinion t3 through segment et. Someengine manufacturers desire to have a power control unit which will givemanual control over a low range only of throttle opening, for example,during the se-called taxiing range, which is equivalent to control leverpositions from idle to a position slightly below that for minimum cruisepower. If such limited manual control is desired, is only necessary toprovide cam-10 witha contom` such that it will call for manifold presures'which are Llower than can be obtained byimanual control -for thatpart of the main con.- trol 'lever .'travel,` butwhich, when va settingapf proximating minimum cruise is reached, will equal the settingobtained by manual control of the throttle. From this point on, thecontour or" cam le will call for manifold pressures greater than canobtained through manual control of the carburetor throttle, so that thesettings are obtained automatically.

Loosely mounted on the main shaft di, or mounted for relative movementwith respect to said shaft, is a lever 9? having an angular portionabove and to the left of the shaft :il dening a stop 953'; and thatportion 4t2 of the lever l2 Which carries the pinion gear Its isprovided with an adjustable stop 9| adapted to engage the stop su whenthe throttle valve reaches a predetermined open position. The lever 9uhas a depending knob or ballhead adapted to engage in a recess or slotprovided in the adjacent adjustable extension S2 of a valve 92, saidextension overlying the stem of a valve 93 having thereon an upstandingboss or projection 93. Valve 92 is normally urged toward its left-handposition, as shown, by a spring 9d. The stem of valve 93 continues on tothe right under the extension 92 and has its upturned end spaced fromthe downturned end of said extension, to provide a lost-motionconnection 95 for a purpose to be described. A spring Sd normally holdsvalve 93 to its leithand position, as shown.

Valve has a land g which is adapted to close oil'` channel P-/i acrossthe valve and hence oil from cylinder 5s when the throttle is in wideopen position, and another land Q? which is adapted to close on" highpressure oil to a Warinup drain bleed when the throttle reaches wideopen position and which will later be described. It is desirable to stopthe travel of piston 5 l when the throttle is wide open since at thattime the carburetor throttle I@ will be holding the lever ft2 and pinion43 against further movement to the `I`ight, and if the piston 5| thenhas full oil p ssure exerted thereon, the resulting force will betransferred through pinion d3 and the internal segment fi-5 to levers5i-5 and l5 and tend to move the latter to a lower setting. If thepistons 5|, 5| were stopped just before wide open throttle is reached,it would not disturb the setting of the power lever, but since this maynot be the case. the valve 93 is preferably moved to the right untilliust before Wide open throttle is cuts oil pressure to 5|, stoppingtravel of the throttle piston assembly pre-venting the action abovedescribed.

The of the piston cut-off valve 92 is based on throttle position. lf thethrottle opens too far. the valve completely closes, cutting off oil topiston. chamber 53. Spring 5 will then tend to move the pislons 5i. Elto the left, oil bein@ forced from chamber 53 through bleed 99 to drain.(Note that there is also a circulation bleed in piston 5|.) However, asthe throttle start moving back or to the left, the valve yrts openingii-ressure PW?? is huilt up piston chamber 53 to hold the pistons openor to the right. Thus the pistons will be stopped when. cut-oir. valve92 is pcsitionedto supply P-d pressure to chamber 53 suiicient to holdthe pistons in balance with other existing forces. A negligible motionof cut-ori valve 92 and conseouently the pistons il bl in eitherdirection will then produce suflicient change in such pressure tobalance any possible variation in forces on the pistons, so that as longas the main servo valve supplies the necessary Pme pressure, the throt-rtle will hold a substantially fixed openposition as determined by thecut-01T valve. Reaction 10 forces tending to reset the datum may beavoided by attaining such xed open position before the throttle i6 hasopened far enough to contact the stop I6.

Valve 92 has a land 98 adapted t0 close oi communication ports P-S' andELS" up until the throttle reaches a certain position, for example,threeefourths open, after which it communicates said ports and permitsiiow of high pressure oil to hydraulic piston il, to be clescribed.

Control of hydraulic couplings When throttle approaches its fully openposition, lever it iirst moves valve 92 to the right due to lost motionconnection at Q5, opening communication between ports P- and P-B", andthen it also moves valve 93 to the right, stopping travel or" piston 5|,5|. Upon further eX- tension of aneroid 58 due to a further decrease inair density, lever moves valve 55 suiiiciently far to the left to permithigh pressure oil to flow from P-Z (right-hand branch passage) to PaS,whereupon high pressure oil ows to cylinder it (Figures 2 and 6) inwhich piston is mounted and has connected thereto a uid coupling oilmetering valve |62. As valve |2 moves to the left, it uncovers a seriesof metering orces |83 formed in the wall of a cylinder H34. The actionof these metering oriices is generally similar to that of a meteringvalve; in practice and as shown in Figure 6, they consist of a series ofholes formed through the walls of the valve cylinder and arranged inspiral or screw formation and of gradually increasing flow capacity, orin a manner such that there is an increase in oil or iluid delivery insubstantially direct relation to the linear movement of the valve. Highpressure oil may pass from chamber H35, through axial passage or hollowcenter GS of valve |02 and out through ports llll into space |68, fromwhich it flows through the metering orifices |63 as the valveprogressively moves to the left and out through ports |09 and intochannels P-'l and Each position of the valve le? corresponds to a deniteoil flow to one or more of the couplings and hence corresponds to adefinite supercharger speed and a definite manifold pressure (assuming agiven condition of night). In order to maintain this predetermined flowrelationship irrespective of variations in operating 'Fluid pressure,means in the form of regulator valves and H2 are provided formaintaining a constant pressure drop through each port |99 and Htl.These regulator valves may be of any preferred type; as here shown, eachconsists of a cylinder l It in which a piston lili is slidingly mountedand is adapted to control a port l E for the regu lator valve H2 and H5for the valve H3. Each piston is urged toward closed position by aspring H5 having a substantially low spring ratel so as to maintain asubstantially constant diierential across the valve. Thus, should thepressure of the engine oil system (I3-2) vary due to wear or othercauses without a like varation of P-l or P-l, or should the pressure onthe P-i or P-Q side of the valve vary at a given pressure of PM2, thediierential across the pistons il i will vary only momentarily until thespring llt reestablishes the differential.

Operation o f coordinated throttle und hydraulic coupling control i itsrange of angular'travel, the valve QIwillb ginV to'open and communicatethe ports andPi-w. When' the throttle is be'- tweenthis position andWide open, valve 55 can admit highpressure oilP-Z into channel P-i-l andthence to cylinder itil and cause movement of piston'il 'to the leftcarrying valve EGE there-- with4 As the valve 162 'moves'to the leit,oil 'ist 'starts metering intochannel PJ?, across the port `l I5 andthence into feed oil channel P il which feeds oil into conduit 3i to thelow speed coupling 36. As the pressure increases in this coupling-,thespeed of the superchargerli vcorrespondingly increases and builds up theinanifold: pressure toa valuecorresponding to the setting-'ofthe powercontrol lever 45. increasinguthedatumsetting and/or increasing altitudewill tendto further open the servo valve 55 and increase fthe 'pressurein channel P-t, causing the valve-lZ'toprogressively move to the left,uncovering-'the metering oriiices m3 and rst-metering( oil to thelowpressurecoupling through channel l2-l and then to the highV speedcoupling? through channel 1?-9.Vv When the1 oil fiow P'i'islgreat enoughto drive the low coupling 2li atl minimum slipand the oil ilow P490 tohighicouplingil becomes great enough to drive the supercharger at evenhigher speed, automatic engineva'lve 38 will cut oi line 3icomniunicatingPS to low coupling 2i. Preferably, there-'isapredeterminedamount of overlap betweerrthe portsfiii'and H9 so that aminiinuin travelwill be required of valve 92 between the pointswhere-.oil flow PLS'drives low coupling 2'! at minimum" and where oil 'flow P-ii isgreatfenough to cause high coupling il" to overdivefand close valve 3%.:Further increase in the supply-or oilto the high speed coupling will fuith'eraccelerate'the-supercharger lf3 until a maxi mumfsupercharger speedreached at minimum slip or the high .speed coupling.

Theraction of the aneroid 5S is basically the samel inhoth control bymanipulation'of the throttle and by feeding oil to the variable speedcouplings for the supercharger ifi. When the throttle is wide open, theservo valve by varying the feed of oil to the conduit lD-E, positionsthe coupling valve lili linstead of positioning `thepistons 5i, 5iandthe carburetor throttle; Should the manifold pressure temporarilydecrease at a given datum setting, datum spring S3 will pull the'shaft38 to the right, moving servo valve 55 to the left venting high oilpressure through the channel 5?-5 to the end of'piston les. the valve N2moves to the left and increases the driveon the supercharaer 14j thelatter will accelerate until the manifold pressure'is restored to itscorrect value, whereupon the aneroid 5S' acts-to' restorev the servovalve"55'to`its normal position and reduce the vv of oil to the pistonlili, thus stopping the travelof the valve EQ2 and holding thesupercharger speed at a point necessaryto maintain the manifoldlpressure datum setting as determined by theposition of power controllever 45. Should the'mani'fold` pressure temporarily increase at a givendatum setting, the travel of the servo valve 55 will be to the right,whereupon oil pressure tothe right of piston IBI in the cylinder Hill-isbled out through channel H1 and bleed H." instead`of being vented by theservo valve E to the oil drain channels-P43, andthe valve H32 isreturned 'or moved to the right.

Since there is a' range in which the manifold pressure: is controlled.bQthYbyfthe. carburetor throttle make w someV provision so that ways gowide open before a the throttle will al# partially open equilibriumpositionof the coupling valve H32 can be obtained. For this reason,Awhen the servo valve .iis positioned toimaintain holding pressures P-:iand P-Ei on the opposite ends of pistons 5l and 5| and thecarburetorthrottle is stopped at less than wide open position, the couplingcontrolla-nd on the sevo valve i'is located so that thepressuretransmitted to piston 10i through channel PLS cut ofi from high pressureoil iirchannel-P-Z. However, aslight displacement or" 'hefservovalverrorn this equilibrium position willthen' feed 'high pressure oilto the channo"P`- E1which operates the-piston EG l. As a resulttheremayjoe a slight shift in the neutral or normal position 'of theservo valve when a change from'regulation by way oi carburetor throttleto regulationv by; way of the oil coupling controlv valve '02 takesplace. This shift should be very slight andI will correspond to averyslight change in' the manifold'pressure setting, say for exampleabout'one-fourthY inch Hg. Thus, in the range' between; for example,three-'fourths throttle opening to wide open throttle= the latter willcon'- trolthe setting 'of the valve .5.5 and any'equilil riurn' positionthereof wlllhorrcspond to a closed position of the coupling controlvalve |02. However,` the' coupling control valve' is always ready forprompt response when acceleration is desired:

StabilityA and' damping system4 InV order to maintainan optimum boostcontrol response characteristic that mayresult from a too rapidresponse, it is desirable tor provide means for combatting any tendencyof the control to surge. For the coupling control' valve IGZ; it may bedesirable to have a relatively rapid travel to the left or in an openingdirection, which suitably-Calibrating the servo ports whichicontrol theadmission of high pressure iluid` tothe piston 10|. On the other hand,return' travel of the valve H22 may be much slower, whichl maybeVregulated. as desired'by suitably. Calibrating' thebleedll'. Should theaction of the valve |82 result in overspeeding of the supercharger I4 toa point where it tends to raise the manifold pressureP-I above a givensetting of the datum control, the carburetor throttle will act toholddown the manifold pressure by.. moving, toward the superchargerslows down and again takes over. When the supercharger is beingdecelerated,.if yit should underspeed and produce too low manifoldpressures in the high power range, the carburetor throttle being alreadyat or near wide open position, is not able to immediately correctby-further openingbut it can rapidly lower the manifold pressure in theevent the valve |02 is too slow on itsreturn.` Hence vthe coupling valvemaybe permitted a relatively slow return movement;

However, additional dampmg and stabilizing means may be necessary, andin thecontrol unit as shownin Figures 2, Band 4, the throttle pistons5i, 5H, coupling valvepiston lill and aneroid 56 areclamped in' a mannersuch as to prevent the manifoldfpre'ssure from overrunningor-overshootinguwhenf-it approaches a givenidatum setting.

In cylinder 52.-is mounted a smallr'cylinder |20;- andpiston .5i hasconnected .thereto ',aJdamp.:

and `the oil'couplings,A it is desirable to' andy to avoid instability'can be accomplished by. lands and coactinga. closed position until,

lf3 ing piston |2| mounted to slide in the cylinder |20. A channel |22communicates the cylinder I2@ with the cylinder |00 on the left-handside of the piston Isl, and cylinder Iil communicates with cylinder S8by way of channels |23 and |24. In this manner, the damping pressure P|3in back of pistons |2| and Iii! is vented to the space in back ofdamping piston 58 for the servo valve 55. A bleed communicates channel|23 with the drain system, and hence a pressure is developed on piston8S' which varies with the rate of travel of pistons 5|' and/or valvepiston ml, and this force is carried through spring 3l, servo valve 55,servo lever 85 and shaft or rod 68 to the aneroid 56 and produces achange in datum setting in the same manner as does a change in loadingof the datum spring 63. When pistons 5|, 5| and IGI are not in motion,piston 88 returns to its equilibrium position (the position shown) andrelieves the resetting load on aneroid 5t, so that the normal settingagain governs. Thus, when the manifold pressure appreaches a given datumsetting, the latter is ternporarily changed to meet the manifoldpressure.

As the manifold pressure then starts to overshoot n this false setting,the latter will return to the correct setting as determined by the datumcam lil at what might otherwise be the peak of an overshoot curve.

The diaphragm 53 also places a load on the aneroid SS whenever themanifold pressure is changing rapidly. Here again a temporary resettingforce is produced tending to change a given datum setting. The rightside of said diaphragm is exposed directly to manifold pressure P|,while the left side thereof, chamber 5l, is vented to manifold pressurethrough restriction 26. Thus, when manifold pressure changes rapidly,the pressure P-Il in chamber 5l will lag behind the manifold pressureP-I, and this lag acts as a force tending to momentarily change thedatum setting. as the manifold pressure approaches this false setting,it stops changing and the pressure P-l l will equalize with pressureP-I, thereby cancelling the resetting` force.

Cruise override with common lever for selecting manual control Incertain power plant installations, it is desired to have a plurality ofpower settings available to the pilot within the cruise range; forexample, one for cruising at relatively low brake mean effectivepressure for best performance, and another higher brake mean effectivepressure for best fuel economy.

ln the invention as herein disclosed, cruise override control preferablyhad by a lever i3!) separate main power control lever 45, ent being suchthat the pilot has complete control by the main power lever irrespectiveof the position of the cruise override lever. Lever i3d is connected bylink |3| with lever |32 journaled on, or mounted for rotative movementby means of, a pin or stub shaft |33 carried by the housing Gil. Alsomounted on shaft 33 for movement relatively to lever |32 is anotherlever iifi which has a bell crank arm constituting a contact member i3d.A preloaded leaf spring 335 partly encircles the shaft 33 and at one endbears against an abutment |36 forming part of lever ifi? and at itsopposite end 'engages the contact arm is the said abutment 36 beingadapted to engage the lever i355 when lever |32 is rotated in acounterclockwise direction. It will be seen that when the lever |32 is14 rotated counterclockwise, there is an impositiva or resilientconnection between it (lever |32) and lever |34, but when lever 32 isrotated clockwise, it has a positive turning action on lever |34.

The lever heretofore described is extended upwardly and provided with acontact |31, and when lever |32 is rotated counterclockwise, |34 engages|37 and raises cam follower il clear of datum cam lll, at the same timeincreasing the manifold pressure datum, which acts back through servovalve 55 and pistons 5|, 5|' to open the throttle. rIhe counterclockwisetravel of lever |32 has a predetermined limit corresponding to maximumcruise manifold pressure. Should the main power control lever l5 be setat a point above the setting of the cruise override lever 30, cam "iiiwill again contact cam follower l| and move contact |31 clear of |34. Onthe other hand, should the main power lever 45 be set at a point belowminimum cruise position of lever i3d, as for example idle position, camfollower 'i3 will engage cam 'Hl (which is integral with datum cam 1Qand also turns with lever 45) and turn lever il clockwise until camfollower fil again rides on cam lli, the diierential motion betweenlevers |32 and |34 being taken up by spring ld. Thus, the cruiseoverride lever does not have to be moved from any given overrideposition in order to get manifold pressure settings by the main powerlever above maximum cruise setting or down to idle setting.

Should the pilot wish to throw the control unit into full manualcontrol, lever i3@ is turned to its extreme right-hand position, causinglever |32 to turn lever |315 to a point where its free end engagesplunger |39, and the latter then acts through rod Iii) to close valve 89and shut off operating fluid from servo valves 555 and 84, whereuponpistons Si, 5| will be forced to the left by spring lill and manualcontrol is had in the manner heretofore described. Plunger |35? isnormally biased to return position a spring Uil.

Manifold pressure limitation under charge heating conditions In certaintypes of engine installations, notably single stage engines where nocooler or intercooler is employed, it is sometimes deemed desirable toset an upper limit on the manifold pressures which the automatic controlcan produce at the highest supercharger rise ratios, or at highaltitudes where the diiferential between air inlet or scoop pressure andmanifold pressure attains its highest value for a given speed of thesupercharger, since under these conditions, there is considerableheating of the charge and this may result in severe detonation anddamage to the engine.

The right hand or free end of datum rod or shaft t8 slidingly projectsinto a bore formed in the adjacent end or a Contact and guide rod M5,the latter being formed with an enlargement defining a shoulder againstwhich the one end of a spring istil abuts and serves to normally urgethe said rod lfi to the left in abutting el gagement with the datum rodor shaft A itting it? is threaded into the enlarged end of rod ist andclampingly engages the central portion or" a balance diaphragm |158forming a movable wall of a manifold pressure chamber |58 andfunctioning to compensate for oil drain pressure (P-) acting on theright-hand side of sealing diaphragm BS. The outer free end of the rod|55 is adapted to engage a roller |513 carried by aelever. 5| pivotallyanchored at its upper. end to a depending lug .formed on the adjacentpor-A tion of the housing Ll. The lever itl depends into an: elongated.chamber or passageway |52 and` at its lower end is provided with aroller engaging in a recess formed in a yoke-shaped tting |53 secured onthe outer end of a rod |554. A- diaphragm |55 forms a movable wallbetween ascoop .pressure chamber |55 and the lower extremity of .chamberor passageway 52 and may be vented to scoop pressure by means oipassageway l? and pipe or-conduit |53. The central portion of diaphragm|55 is clamped between a pairof reinforcing and stifening plates whichare in turn. clamped between the member |53 and a bushing i552, thelatter at its left-hand end projecting into the adjacent enlarged end ofa cylindrical member itil and a sealing diaphragm |6| being clampedbetween the bushing E59 and member itil at this point. A sleeve |52 isslidingly telesooped on the member |53 and is normally urged to anextended position toward the left by aspring 53. .Another weaker springIflis disposed around the flanged extremity of sleeve |52 tohold theparts of the assembly against looseness and rattling.

Mounted for sliding movement in a boss or projection formed on thehousing lil are a pair of datum limiting rods 256 and i's', each havingits free left-hand end provided with a threaded -A extension foradjustability. The rod is of two-part construction with one parttelescoped over the adjacent end of the other and having a spring |63interposed therebetween; and at its righthand end, said rod it the upperend of a lever it, i'ulcrumed at il@ and at its lower end engaging in ayoke-shaped extension of the sleeve |52. The rod l? has its right-handextremity notched for receiving the upper ball-shaped end of a lever lliwhich is fulcrumed at Il? on a relatively stationary' lug |13, said rod|61 being normally urged to its left-hand position by a spring Hfs.

Manifold pressure is conducted to chamber or passageway |52 and thenceto chamber by way of conduits having the pressure desigM nation P-I asshown.

The terms manifold pressure droop or altitude droop as used herein referto the action which takes place when the differential between manifold pessure and scoop or atmospheric pressure attains a certain predeterminedvalue and at which time the load on the aneroid 5t is reduced for agiven datum setting relatively to what would normally be the load werethe altitude droop mechanism not used. This so-called drooping startswhen the differential on diaphragm 55 becomes sumciently great to moveit to the left until lever i brings roller |5|l in'to contact v" theadjacent end of rod Ulli. l now scoop pres sure further decreases at agiven datum setting, the diaphragm |55 will act through lever 5| anddatum shaft S8 to lower the datum or manifold pressure setting,

said diaphragm having its effective area proportioned to cause thisresetting force to give the required droop.

Figure l plots manifold pressure against scoop pressure (which couldalso be altitude). Let it be assumed that curve llt represents aposition of the main power lever si?. which calls for a datum setting onaneroid 55 or" fifty-four inches manifoldjpressure and which maycorrespond to take-off power settings or power settings short ofwaremergency settings. As long as lever remains `in aposition such 4thatroller |50 out is in contact with ric of contact with .rod |45, .the`manifold pressure will be maintained constant with respect to scooppressure, but when roller contacts said rod, the force of the expandinganeroid bellows as determined by the datum spring is not onlycounteracted manifold pressure but also by the differential acrossdiaphragm |55, resulting in the break at theright extremity oi curve|16. The scoop pressure'at which. this breakl occurs maybe controlled byregulating the load on spring |53, which determines at what value ofscoop pressure lever |5| will bring roller |553` in contact with rodHl.y For the manifold pressure range below the break in curve |15, pushrod E56 is in contact with piston Gil and said rod .then actsthroughlever |59 lto position slid-l ing sleeve |52 and vary the load onspring` |63; suitably proportioning the lever ratio of lever its inaccordance with the rate of spring |63, the load on diaphragm may bemade to vary with respect to av given sea level manifold pressuresetting in a manner such that drooping will start at a predetermineddifferential betweensooop pressure and manifold pressure. The dottedlines I'E'i represent sea level settings of. the power control leverbelow take-oil power; they carry out to where the droop line occurs incurve H, from which point they will follow' |73 out to maximum altitude.

For power settings above take-oli, for example; the setting ofsixty-five inches represented by the full line curve |18` andintermediate settings represented by the dotted lines |19, it becomesnecessary to increase the load on springv 63 to compensate for or equalthe increase in manifold pressure exerted on the left-hand Vside ofdiaphragm |55- above that for take-oif power settings, in order thatlever |5| will take a position similar to that taken at the lower ettingat a given scoop pressure, or will act on rod |45'at the same scooppressure and promote the droop at the predetermined point in the curve.This ispdone by push rod |61, which is adjusted to contact piston k(lllwhen the latter reaches a posi# tion corresponding to take-off manifoldpressure, here shown as fifty-four inches( absolute). For settings abovethis (curves |18 and |19), push rod |61 acts through lever I'll to movelever |69 independently, spring |68 taking the compression on push rod|66. Lever is proportioned to producethe change in load on spring |63necessary to start drooping at a fixed altitude for main power leversettings above take-off.

In actual construction, the special parts required for altitude droopare all mounted in a manner such that they can be removed or replacedasa unit. This is of advantage due to the fact that only certain types ofinstallations require this special feature.

Engine speed or R. P. M. control The propeller pitch governor setting,and hence engine speed, is controlled by angularly positioning a shaft|8|, Figure 5, suitably journaled 4in the housing 4G and having securedthereon an arm |32 connected to the propeller pitch governor lever 20 bylink |83. Also secured on shaft |8| is a segmental gear |34 in mesh withthe toothed portion of a rack bar |85, the latter being prof vided withan extension slidably supported ina `bea-ring |86 which may be integralwith a wall |81 formed as part of the housingV dll. The toothedextremity oi the rack bar preferably has bearing on a roller Itssupported by a stili; leaf spring or likeresilient member to ensure fullmesh l i? of the rack and gear teeth and avoid backlash due to wear orplay in the parts; and the extension I 85' is preferably connected tothe bar proper by a hinge pivot member |89 to compensate for any slightmisalinement that may develop during use or result from inaccuratemachining of coacting parts.

A servo piston |90 is connected to the rack bar extension |85' and issiidingly mounted in a cylinder ISI. Operating fluid (P-2) for piston|90 is conducted to cylinder I9I at opposite ends of piston |90 throughports or passages |92 and I 93 controlled by a servo valve generallyindicated at I 94 and comprising a bushing |95, defining a valvecylinder |95 in which a valve member |96 is slidingly mounted and has acentral land I 91 and two end lands |99 and |99. The left end of thevalve member |96 terminates in a stem portion which is encircled by aspring 200 normally urging the valve member to the right into abuttingengagement with the adjacent end of a rod |96'. The bushing |95 ispreferably made in sections to compensate for inaccurate machining, andlikewise the valve member |96, being separate from the rod |96', alsopermits any slight misalinement.

A lever (see also Figures 2 and 4) carries at its one end a cam follower202 adapted to ride on the cam 41 which is rotatable with the lever 45".fulcrumed or pivotally mounted at 203 on an upstanding lug which may beformed on the housing said lever 20| having a bell crank extension orarm 204 to which is pivoted a servo lever 205.

When the pilot moves lever to a selected the main power control powersetting, he rotates the lever 95 which carries the cam d1, and thelatter, acting through the lever 20| and servo lever 205, positions theservo valve I 9S. If the cam 41 is rotated in a counterclockwisedirection (datum increasing direction), the servo lever 205 is moved tothe right, whereupon the valve |99 also moves to the right and the land|91 releases high pressure fluid (P-2) to the passage |92 and cylinder9| to the left of the piston |90, while at the same time land |99permits fluid to drain from the cylinder |9| on the right of saidpiston. This moves the piston to the right, thereby swinging the arm |92to the left or in a direction'to reduce the pitch of the propellerblades and increase engine speed for a given power lever setting. If thelever 45 is moved in a clockwise direction, the servo lever 205 is movedto the left, thereby also moving servo valve |99 to the left, whereuponthe land |91 admits high pressure iluid to the passage |93 and thencethe cylinder 9| on the right side of the piston |90, while at the sametime oil may drain from cylinder i9! on the left side of piston |90, thelatter moving to the left and rotating lever |82 to the right or in adirection to increase the pitch of the propeller blades and decreaseengine speed for a given power setting. Thus, for each position of thepower control lever, a denite engine speed may be established accordingto a curve determined by cam 41.

Due to the high tolerance in the slope of calibration curves fordiierent propeller governors, it may be necessary to make someadjustment at installation to obtain a stroke of the servo lever 205such as will give the required power control angle vs. engine speedcharaceristic. Such adjustment should have no eifect on the maximumspeed setting 'out should have a proportional The opposite extremity oflever 20| is gradually increasing eiect for engine speeds as the latterapproach the minimum setting. An adjustment which meets the foregoingrequirements consists of a pair of floating links or arms 206 and 208pivotally connected at 201, the arm 208 being slidable in a retainer andguide 209 carried by the upper end of the servo lever 205. The upper endof the arm 206 is formed with a slot 2|0 extending at substantially aninety degree angle to the said arm. A fixed but angularly adjustablemember 2| I, note Figure 7, carries a pin 2I2 which engages in the slot2|9, the said member 2| being formed on the inner end of a screw stub 2|i' which projects through a ring 2I3 on the upper end of a boss formedon the rack bar |85, said screw stub having a screw slot in the outerexposed end thereof. The contiguous surfaces of the disc 2| I and ring2I3 are provided with matched serrations, and a spring 2 I3 pulls thedisc 2 I against ring 2 I3 with suiiicient force to prevent angular orrotational movement of the disc 2II under normal operating conditionsbut permitting angular adjustment manually by means of a screw driver orother suitable tool.

To adjust the stroke of the rack bar |55, the contr-oi lever i5 may beset at maximum power position and the linkage .and coacting parts whichconnect the said lever l5 to the governor control element 20 adjusted togive the required maximum engine R. P. M. for the power output at thisposition. The servo lever 225 should at this time be located so thatrelative movement between the servo lever and member 2H or the pin 2I2carried thereby will not aiect the position of said lever, or willsimply result in relative up and down sliding movement between lever 205and arm 208 without materially affecting the angular position of theservo lever, but for the minimum speed position of piston i952 (theextreme left-hand position), and for a corresponding position of theservo lever 295, relative movement between the servo lever and said pinvaries the angular position of the servo lever and consequently variesthe setting of the servo valve or the action of the servo lever withrespect to the valve. For positions between minimum and maximum speeds,the eiiect of the adjustment is proportional, the angle dened by thearms 296 and 299 gradually decreasing as the rack bar moves to the rightand attaining a minimum or becoming zero as the maximum R. P. M.position of the lack bar is reached.

In the event of failure of oil supply to the power control unit, it isdesired to have the propeller governor automatically take up a positionfor a given predetermined engine speed at any setting of the pilotscontrol lever at or above that which would result in a power outputsuiiicient to maintain such predetermined speed at minimum pitch of thepropeller blades. For example, the governor may be automatically set foran engine speed of 2400 R. P. M. should the oil supply to the powercontrol unit fail during flight or take-off er at any power settingsuiiicient to maintain the aircraft in night.

With this in view, a cylinder 2id is disposed in alinement with cylinderI9I and a pair of coasting pistons 2|5 and 2H are mounted to slidetherein on the extension |535 of the rack bar |35. The space between thepistons is vented to oil drain by means of ports Eil and 2I'I formed inthe shaft which constitutes said extension. One or more compressionsprings 2I0 are `disposed between the pistons and normally `urge thelatter apart.

.member 22e adapted A channel .2!.9 communicates high pressure fluidto-the cylinder 2id at opposite ends of the piston; and as long asoilpressure remains normal, the pistons will be closed or remain in theposition shown in Figure 2. The piston Sie is Ydished and carries a hubto vengage a stop4 shoulder 222 formed on the extension |85'.

Should oil pressure fail, the springs 2i`8 will separate the pistons 2idand 2|6 and thelatter will move in opposte directions until ypiston 2 i5reaches the limit of its travel to the left and the Vhub member 220engages the shoulder 221 on the extension 55'. The thrust of piston 2|6then acts through .the rack bar its to position the shaft lill inamanner such that the propeller pitch governor will be set in a positionto give the desired pitch angle to the propeller blades. Assuming it isdesired to reset the propeller'blades to a pitch angle such aswillresult Yin an engine speed of 24:90 R. P. M ,at minimum cruise poweroutput, .then the shaft i3! would be positioned to set the pitch of thepropeller blades through Vthe control element 2B to ,give this speed atthe minimum cruise position of the pilots control lever d5. Should thepropeller control governor Iii be of the hydraulic type re- .ceivingr asupply of oil or hydraulic fluid through Vthe power control unit, thenthe shaft it! may bepositioned to bring the propeller pitch controlelement to its low or high stop, whichever is desired. Ordinarily,however, the propeller pitch governor would be of the type wherein themotivating power is supplied from a source separate from the powercontrol unit, so that the control element would be effective at anyposition within its range of adjustment.

Selection of manifold pressure and engine speed for dz'ierent take-o1?power settings Means are provided whereby different coordihated manifoldpressures and engine speeds may be had for different take-o powersettings without affecting the normal schedule or the remaining powersettings. For example, an engine may have two take-off power settings,one for part throttle operation at a given manifold pressure and enginespeed, and another for wide-open throttle operation at another manifoldpressure and engine speed.

`First considering the manifold pressure reset, a cylinder 225, noteFigure el, has at the right hand. end thereof a hollow piston 22Eadapted to contact the upper extremity of lever il under conditions tobe described. A bolt 227 projects through the cylinder and piston and issecured to the latter at its right end, and at its left end the bolt isheaded and engages a member 228 which is of open construction to permitoil under pressure to pass into the cylinder. A spring 22S abuts at itsright end against the adjacent end of Athe cylinder and at its left endabuts said member. VPL2 pressure is supplied to the cylinder 225 by wayof passages 233, 235', the passage 233 having its inlet end controlledby valve 93. Communication between passages 239 and 238 is controlled bya valve generally indicated at23l andcomprising a ported cylinder inwhich is slidingly mounted a valve member 232 biased to closed positionby a spring 233 and carrying at its right-hand end an. adjustablecontact screw 234 adapted to be engaged by a cam surfaced contact 235formed on the gear segment d5. Since the gear 46 rotatescounterolockwise when the power lever 45 is moved in a power-increas-,ing direction, contact .235 will engage 234 at a `predetermined power`setting (which may `be at part or substantially full settingof the mainpower control lever,depending upon adjustment of contact 234i) and openvalve .231, and since at this time the entrance to passage `239 is stillopen, P-Z pressure will be communicated from passage 23S to 2% andthence into cylinder225 and hollow piston V226, .forcing .the `latter to,the right against the tension of return spring229.

The lever 'il .has ,an elongated slot `23S for pin .l5 which extendsatapredetermined angle, so that when piston 22% contacts lever ll, it canmove the latter vclockwise about the pivot pin i3 without affecting theposition of lever l2 until the playin the slotis taken up; and thislimited movement acts through link 86, rservo lever fifi and servo`valve 8d to relocate datum piston Sli slightly .tothelefig therebyreducing f the datum and tending to close the throttle. Ilhis resultsina manifold pressure setting lower than that which would lnormally belproduced by cam lil. The return spring for servo valve til maintainslever 1.1 in its :normal position whennot contacted lIcy piston V26.

Resetting of the propeller or engine speed governor may be obtained inthe followingmanner:

The lever2ll is provided with an arm-23l,see Figure 5, which extends.beyond the ulcrumor pivot 203 and carries a vroller .238 engaging abracket or yoke iekconstituting anextensionof a piston v239 mounted toslide in a cylinder v2li!) against the tension of apreloaded spring 24|.An adjustable contact 242 determines -the limit of downward travel ofpiston 239. Dowmvardor clockwise (speed-increasing) movement of varm23'! is produced by a piston243 slidingly mounted in a cylinder 2M andbiased to inactive or return position by a spring .245, the said pistonbeing provided with ,a bleed 246 to\' permit proper return movement whenthe operating pressure is relieved. Operating pressure is supplied tocylinder 24a' by way of a passagerZll which branches off from passage239', see Figure 4.

Let it loe assumed that there is a requirement for two take-oisettingsfor an engine, one "for part throttle operation with an engine speed of,for example, 290013,. P. M. andfty-two inches Hg manifold pressure, andanother for wide-open throttle loperation withian'engine speed of '2800R..P. M. and fifty-four inches Hgmanifold pressure, the change to theserespective engine speeds and manifold pressures to take place only attake-off settingsof the `power control lever l5 with the remainingsettings thereof conforming to the normal schedule as determined by the-respective contours of cams 4l and if). For part throttle operation,the screw 23!! `is `adjusted so that when the lever 45" is rotatedcounterclockwise vto a point where the take-oir setting .is reached,contact 23 5 will engage234 and valve;232 will be moved to the left,permitting oil under pressure (P-2) to pass from conduitor passage 22E!to 230 and thence to the cylinder 225; this pressure being alsosimultaneously transmitted to the cylinder 244 through passage 24's.Piston 225 now moves to the right and contacts'lever 1T, movingsaidlever `clockwise until the clearance at 23o is taken up. Thisrotates `lever -T'I about the pivot 'i3 without disturbing the settingof the lever '.'2,.while at the same time it acts through link ,80 andservo lever 33 to move the servo valve 84E to the left, cutting down thepressure P-i to the left of the piston 64 so thatthe latter will moveslightly to the left and reset the manifold pressure datum. At the sametime, the piston 243 moves downwardly in the cylinder 244 until itslower free end contacts the extension 239' of the piston 239, whereuponthe arm 231 is moved downwardly, turning the lever 23! clockwise andincreasing the engine speed the required amount, depending upon theposition of the contact 242. Should the power lever 45 be now moved to asetting below take-oit, contact 235 will move clear of 234 and valve 23!will close, cutting off high pressure cil to passages 230 and 247, andpistons 226 and 24'3 will move back to idle position, the operatingfluid or oil passing through the bleed 246 into drain oil space withinthe housing lill.

Should the power lever 45 be moved to a setting beyond the take-oirposition, and which would normally happen only for temporary emergencypower settings, the servo valve 93 would be moved far enough to theright to close ofi pressure P-2 from passage 2150, thereby shutting offiiow of oil to the valve 23|.

water (anti-defonce@ fluid) injection override For engines equipped witha Water injection system, it is permissible to use higher manifoldpressures when water is being injected than under normal or dryoperation. However, if higher manifold pressures are used with waterinjection, it is desirable to provide means Where by should the watersupply become exhausted,

the manifold pressure will be returned to normal or a safe value for dryoperation.

The valve 23! is provided with a special land at its left end whichcontrols communication of pressure (P-2) from passage 25e to 25S', thelatter leading to a water injection solenoid valve, generally indicatedat 25, and which may be wired to a pressure switch, not shown,controlled by water pressure in a manner such that as long as water isbeing injected, the valve will be open, but should water pressure fail,the valve will close. For a valve operated in this manner, reference maybe had. to the copending application of Stanley B. Smith et al., SerialNo. 533,296, led April 29, 1944. Also, the valve may be operatedmanually, if desired. Said valve 25! is provided with a valve member25!l which when the valve is closed, shuts off communication between thepassage 25u and a passage 252 leading to a valve cylinder 253 having apiston 254 at its left end adapted to engage the lever Tl when operatingpressure is communicated to said cylinder and piston. The piston 254 ishollow and has connected thereto a bolt 255 having an open type washer255 at its upper end, the said bolt being encircled by a return spring257. This piston and cylinder unit is similar to the assembly comprisingthe cylinder 225 and piston. 226 heretofore described.

When the power control lever 45 is set for a power requiring waterinjection (which is usually an emergency setting above take-off powers),the contact 235 will have been rotated to a point where it will open thevalve 23h the exact point being determined by adjustment of 234,whereupon oil under pressure (P-2) will be communicated from passage 25!to 250'; and assuming that the solenoid valve 25l has been turned on,valve member 25i will have moved upwardly a sulcient distance tocommunicate passage 25u' with passage 252. Oil under pressure will thendow to the cylinder 253 and piston 254 and move the latter to the leftuntil it contacts lever li, causing said lever to rotatecounterclockwise and also rotate the leverlt in a similar direction,raising cam follower 1I clear of cam 'IIJ and at the same time actingthrough link 80 to move servo lever 53 to the right, increasing thepressure P-IE to the left of piston 54 and raising the manifold pressuredatum to give the increased manifold pressure required for waterinjection. The lever l2 continues to rotate to the left orcounterclockwise under the action of piston 254 until the cam follower13 contacts the cam surface i38, which determines the particular valueof manifold pressure for water in'- jection. Should the water fail orbecome exhausted, valve 251 will close, or be returned to the positionshown, cutting oir oil from passage 252. The oil entrapped in the lineor passage 252 will now bleed to drain and spring 251 will retractpiston 25d whereupon the lever l2 will be moved clockwise under theinuence of the spring 'i9 until the cam follower 'H again contacts thesurface of cam lli, the manifold pressure then being restored to itsnormal value. It will be noted that valve 23| will not permit thetake-off reset piston 226 and the water injection reset piston 254 tooperate simultaneously.

Provisions for epedztzng warm-up of the servo system To provide forwarming the control up rapidly after the engine has been started, meansare provided whereby a fairly large quantity of oil may be circulatedthrough the unit during the warming-up period, such increasedcirculation being automatically returned to normal when the throttlereaches a predetermined open posi-v tion, preferably its wide openposition. This is accomplished by providing a bleed 260 from the passage239 to the drainsystem (P-) of the unit. Thus when the engine is warmedup at part throttle opening, the valve 93 which admits high pressure oilto the passage 238 is open, so that the latter passage becomes part ofthe circulatory system of the unit. However, when the throttle reaches apredetermined open position, valve 93 moves to the right in the mannerheretofore described and closes the passage 23u from high pressure oil,and normal circulation is resumed.

Figure 8 Figure 8 illustrates an hydraulic coupling drive for a singlestage engine to which the herein' disclosed power control mechanism may'be' adapted. In this instance, the air intake conduit is indicated atZtl and is provided with a throttle 262 which may be controlled in themanner here# tofore described in connection with Figures l to 5,inclusive. A supercharger is generally indivcated at 253 and is providedwith adrive shaft 254 which may be driven at varyingspeeds from' l anengine-driven shait 2te acting through a of operating pressure and as aconsequence will' simply idle. At altitudes above wide open-'- throttle,hydraulic pressure is build up in the; driven rotor of coupling 26 whichthen over- 'i drives coupling 26E and the latter and coupling.

1.28.8 idle. .At :altitudes :above second critical,

where i-the 'capacity ro l,the supercharger is attained through' the:dri-ve :by 'way of :coupling Aorivvhen the latterzattains a:minimunrsiip opereating condition, yhydraulic pressure is'buiit up inYthe-driven-rotor'offcoupling 268, which coupling 'then :beginsto=overdriveacouplings 266 and 255i.

Obviously, 4two couplings-only may be used, or oneormore Iiiuidcouplingsmaybe used with a mechanical clutch-and the lattereither manually orautomatically 4disengaged when the drive is transferred therefrom tothefluid coupling.

Alternate stability and'dampz'ng system-Figure 9 :shown ,as arenecessaryto ian understanding of the .damping systemand .these parts are illus-'trated schematically. The manifold `pressure aneroid is indicatedat2'i8 andthe datum spring ,therefor -at.2`|.|. .Themain servo.valve2-l2, which 'corresponds tothe `valve r580i Figure 2, connected tothe datum rod by means of a lever 273 'pivoted Yor fuICrumed'at'Z'M,said lever projecting beyond the lpoint Where it is connected -to the-servo `valve stem-:and at its lower irse end terminating ina ball headwhich vengages in an annularly groove or recess Vformed in a resetmember .v2l5 .slidab1e ron a piston rod 218 encircled bysprings 211 and2'e8 and having inner and outer reset pistons 218 and 288 on theopposits-ends thereof'which `ares-slidable in piston chambers 28| .and:282. .Chamber 28% is vented .toa pipe or` conduit -283 'which in'turnis vented to drain pressure A,through a lbleed .'li; while chamber -282is vented to drain pressure.

.The pipe or -conduitf283 communicates v.at its lower endwith .a Apistonchamber 285 having a damping piston 281 mountedtoslidetherein andconnected to theone end of a piston rod 288, the opposite end of .saidrod -being vconnected to a back pressure piston y88 slidable in a pistonchamber which is: of greater-areathan 'the chamber .12.86 fora purposeto bedirected. The .pistons 28'? and 289 move in unison, movement tothe-left being resisted by spring 292and oil or hydraulic fluid whichnormally fills the chamber 288 and may escape `therefrom Y:to Achamber28| and through `bleed28ll. Thezchamber 280 communi- Cates with a:conduit 2.95 qwhich `conducts .hydraulic iuid :from an `hydraulic:coupling lvcontrol valve generally indicated at '286.and whichcorresponds `to `the ,couplingvalve |82 ofFigure 2. Other parts whichare vshown in diagram and have their counterparts in Figure `2 includethe vthrottle-operating piston 291, which correspondsitoipistons ,5L- Iofligure 2,.and the cutein :valve .288 which corresponds to valves 92and SSnfEigure 2. Thereis alsozshown an hydraulic-coupling 299 whichdrivesa sup'ercharger 3.88,the latterbeingsupplied with air through anairintakepassage ,or conduit 38| controlled by a throttle .382, A lever-383 connects` piston 29'! with the throttle andhas a contact .384 onthe lower end thereof adapted to contact cut-in valve 298 When thethrottle-attains fz-predetermined open position.

Incineration, the cut-in valve 298 does not open until `the `throttle38.2 .attains `a predetermined open; position-:depending upon thelocation ofthe contact 364 .with respectto lthethrottle 382 andthe-pistonZS'i. .As long as 'themanifoid pressure isbeingmaintainedWithinfa range controlled by the throttle .and-valve ,298 :is closed,pressure fin conduit V295 and pistoni chamber '29.8 'will be :at faminimum and the :backpressure ypiston v289will`be substantiallyzin theposition shown. :During zthis range of control, the servo valve '2.12lwill vbe damped by the pistons -219 and '280, whichif the force exerted.on lspring 21.1 issuiicientto cause movement .to the left, force oilor,fluid through the bleed 288, or if suchmovementis to'theright, forceoil through bleed 285. When the 'throttle attains a substantially wide,open positionandthe contact288 opens the .valve 288, .oil under-pressure will be metered by coupling valve i296 through the conduit'ZSto 'the fluid Acoupling 299, assuming `themanifold pressure' to bemaintained requires the increasedsupercharger speed.

Assuming the datum spring 427| has been set to maintain a givenmanifoldpressure, and there is a drop from such given value due toa'decrease in air density; 'the aneroid Eflwill expand #and turn thelever 213 clockwisefandioil pressure or hydraulic iiuid will-buildupinthe coupling .2.98, whereupon the speed of the supercharger willincrease and 4start to raise the'manifold 'pressure to the value set bysaid spring. As the-manifold pressure rises, the pressure in pistonchamber y298 also increases, tending to'move the`piston'29 and thedamping piston 281 to the left, which in turn increases the pressure inchamber 28| and tends to turn the lever'213 counterclockwise and varythe datum of bellows 270. Thus, -as the manifold pressure approaches'the value determined by the datum spring2' ,'the'datum s'temporarilychanged to meet the manifold pressure. As the manifold pressure thenstarts to overshoot this false setting brought about by the feedbackpressure developed in piston chamber 28|, the datum will return tothe`correctsetting as determined by the datum spring 21| at what mightotherwise be the peak of an overshoot curve.

It will be understood that no attempt has been made herein tolspeciiically Vdescribe `all of the functions and advantages of whichthe improved control unit is capable, and also that certain changes inconstruction, design and arrangement of the parts maybe made withoutdeparting from the scope of the invention as denedby the appendedclaims.

We claim:

1. For usewith an internal 4combustion engine having athrottle-controlled 'induction jpassage provided with a superchargingsystem ,including asupercharger and a hydraulic coupling for varying theratio of engine-to-supercharger speed. power control mechanism includinga manually operable power control meinbenmeans for regulating hydraulicflow to said coupling including a fluid metering valve, hydraulicmotormeansincluding an hydraulic piston arranged to operate the.throttle and another' hydraulic piston arranged'to operate said valve,a servo valvecontrolling admission of operatingvpressures to saidpistons, variable datum means including a device responsive to changesin manifold pressure and an element adjustable by said power controlmember to set the datum for said device, a member movable with saiddevice, van operating connection between said .latter member and saidservo valve whereby the throttle is automatically positioned tomaintainthe selected manifold pressure up to charging capacity forsubstantially wideopen throttle,and af'valvein series'with'saidservovalve adapted to be opened when the throttle approaches'suchpredeterminedposition andpass operating fluid to said :piston `for`operating the 25 metering valve to produce a supercharger speed such aswill maintain the selected manifold pressure.

2. For use with an internal combustion engine having a throttlecontrolled induction passage provided with a supercharging systemincluding a supercharger, a hydraulic coupling for varying the ratio ofengine-to-supercharger speed, power control mechanism including amanually operable power control member, servo motor means including ahydraulic piston arranged to operate the throttle, means for regulatingfluid flow to said hydraulic coupling comprising a metering valve andservo motor means including a hydraulic piston for operating the valve,said hydraulic pistons being arranged in series flow relationship,variable datum means including an element responsive to changes inmanifold pressure and a datum spring adjustable by said power controlmember to set the datum for said element, a member connected to saidelement for movement in relation to changes in manifold pressure andarranged to actuate said servo valve in a manner such as to passoperating fluid first to said throttle operating piston and upon adecrease in manifold pressure at a given datum setting to saidvalve-operating piston, and whereby a selected manifold pressure ismaintained by automatic positioning the throttle until charging capacityis reached for approximately wide-open throttle whereupon said meteringvalve is regulated to meter hydraulic fluid to said couplings, and valvemeans functioning to cut off flow of operating huid to saidvalve-operating piston while the selected manifold pressure is beingmaintained by the throttle but being rendered effective when thethrottle approaches wide-open position to communicate operating pressureto said piston for operating the metering valve.

3. For use with an internal combustion engine having athrottle-controlled induction passage provided with a superchargingsystem including an hydraulic coupling for varying the ratio ofengine-to-supercharger speed, power control mechanism including amanually-operable power control member operatively connected to thethrottle, a fluid-actuated power piston also operatively connected tothe throttle, diierential mechanism arranged to permit actuation of thethrottle by said piston independently of said power control member,means for regulating the eifective pressure in said fluid couplingincluding a metering valve and a fluid-actuated piston for positioningsaid valve, variable datum means including a device responsive tochanges in manifold pressure and a datum spring adjustable by said powercontrol member, a valve-actuatin member connected to said device formovement in relation to changes in manifold pressure, a new channel forcommunicating operating pressure to said throttle-operating piston andsaid valve-positioning piston, a valve controlling passage of operatinguid from said throttle-operating piston to said valve operating piston,a servo valve operable by said valve-actuating member for controllingpassage of fluid under pressure to said second-named valve, and meansbecoming effective upon the throttle attaining an approximatelywide-open position to open said second-named valve and pass operatingpressure to said valve-positioning piston, the arrangement being suchthat said throttle-operating piston acts to position the throttle formaintaining a selected manifold pressure until the throttle attainsapproximately wide-open position Whereupon the metering valve isregulated to meter fluid to said coupling and increase the speed of thesupercharger to maintain the selected charging pressure.

4. For use with an internal combustion engine having athrottle-controlled induction passage provided with a superchargingsystem including a hydraulic coupling for varying the ratio ofengine-to-supercharger speed, power control mechanism including amanually-operable power control member, a fluid-actuated power pistonoperatively connected to the throttle, means for regulating theeffective pressure in said coupling including an hydraulic ow meteringvalve and a fluid-actuated piston for positioning said valve, anhydraulic flow-controlling system including a dow channel for servingsaid pistons and a servo valve controlling now of fluid in said channel,a valve controlling flow of duid from said channel to saidthrottle-operating piston, another valve controlling flow of operatingfluid through said channel from said throttle-operating piston to saidmetering valve piston, means for controlling said last-named two valvesin a manner such that when the throttle attains an approximatelywideopen position Huid pressure is exerted on said throttle operatingpiston in a throttle opening direction and as the throttle approacheswideopen position operating iiuid is passed to said metering valvepiston, and means responsive to changes in manifold pressure foroperating said servo valve.

5. For use with an internal combustion engine having athrottle-controlled induction passage provided with a superchargingsystem including an hydraulic coupling for varying the ratio ofengine-to-supercharger speed, power control mechanism including amanually operable power control member, a throttle lever, a fluidactuated power piston, differential mechanism operativelyinterconnecting said power control member and said piston with saidlever whereby said piston may operate the throttle independently of saidpower control lever, means for regulating the hydraulic flow to saidcoupling including an hydraulic ow metering valve and an hydraulicpiston for positioning said valve, an hydraulic flowcontrolling systemincluding a ow channel for serving the throttle-actuating piston andsaid valve-actuating piston and a servo valve controlling ow of lluid insaid channel, a valve controlling flow of uid from said channel to saidthrottle-operating piston and another valve associated with saidlast-named valve for controlling the ow of operating uid through saidchannel from said throttle-operating piston to said metering valvepiston, said two last-named valves having valve-operating membersarranged in spaced relation for operation in sequence with a lost motionconnection therebetween, said differential mechanism including a membermovable in relation to the throttle, a contact carried by said lattermember, and a valve-actuating lever interposed between said valveoperating members and arranged to be actuated by said contact when thethrottle approaches wide-open position and pass fluid under pressure tosaid metering valve piston and adjust fluid flow to thethrottle-actuating piston.

6. For use with an internal combustion engine having an inductionpassage provided with a supercharger and a fluid coupling fortransmitting a driving force to said supercharger at variable ratios ofengine-to-supercharger speed, power control mechanism including amanually operable power control member, means for regulating the flow ofhydraulic fluid to said coupling in cluding a metering valve and aseries of metering orifices controlled by said valve in sequential orderas the valve `moves towards open and closed position, hydraulic meansfor operating said valve including a fluid-actuated piston, a servovalve controlling flow of operating fluid to said piston, variable datummeans including a cap sule responsive to changes in manifold pressure, amember connected to said capsule for movement therewith, and anoperating connection between said latter member and said servo valve.

'7. For use with an internal combustion engine having an intake manifoldprovided with a supercharger and an hydraulic coupling for transmittinga driving force to said supercharger at variable ratios ofengine-to-supercharger speed, a power control device provided with meansfor metering fluid to said coupling including a first fiow passage forunmetered fluid under pressure and a second fiow passage for meteredfluid forming a continuation of said first passage, a wall forming apartition between said fluid passages and provided with a plurality ofmetering orifices arranged in series relation, said wall defining avalve chamber, a metering valve mounted in said chamber, and means foractuating said valve in a manner such that the said metering orificesare opened and closed in sequence in relation to changes in pressure insaid intake manifold.

8. A power control unit adapted for use with an aircraft internalcombustion engine for maintaining a selected manifold pressuresubstantially constant at varying altitudes including amanually-operable power control member, a variable datum assemblycomprising a device responsive to changes in manifold pressure, a datumspring operatively associated with said device, a fluid actuated powerpiston for ten sioning said spring, a servo valve controlling ow ofoperating fluid to said piston, and means operatively connecting saidpower control member to said servo valve.

9. A power control unit for maintaining a selected value of manifoldpressure in an aircraft internal combustion engine substantiallyconstant at varying altitudes including a manually operable powercontrol member, a device such as an aneroid responsive to changes inmanifold pressure, a datum spring operatively connected to said aneroid,an hydraulic piston connected to said spring for tensioning the latter,a servo valve controlling flow of operating fluid to said piston,linkage operatively connecting said power control member to said servovalve, and followup means operatively interconnecting said pistonlinkage and said servo valve for maintaining said piston at a givenposition as determined by the setting of the said power control member.

10. For use with an internal combustion engine having athrottle-controlled induction passage, power control mechanism includinga manually operable power control member, an 'nydraulic power member forautomatically actuating the throttle, a servo valve for controlling flowof operating fluid to said power member, variable datum means includingan element responsive to changes in manifold pressure for controllingsaid servo valve, said power control member being operative to set thedatum for said variable datum means, differential mechanism providingfor operation of the throttle by said hydraulic power memberindependently of saidpower control member and arranged inra manner' suchthat 28- when said hydraulic power member is located in the region-ofits throttle-closing position the throttle is operable manually by saidpower control member, meansadapted to move said hyi draulic power memberto its throttle-closing position'when operating pressure is relievedtherefrom, and manually operableI means for cutting olf the ow ofoperating liuidv to said hydraulic power member and whereby transferfrom automatic to manual control of the throttle may be had attlie willofl a pilot or operator.

1l. For use with an' internal combustion engine having athrottle-controlled induction passage, power control mechanism includinga manually operable power control member, an hydraulic power piston forautomatically actuating the throttle, a servo valve for controlling flowof operating fluidto said piston, variable datum means including anelement responsive to changes in manifold pressure for controlling saidservo valve, said power control member being operative to set the datumfor said variable datum means, differential mechanism providing foroperation of the throttle by said hydraulic piston independently ofsaid'power control member and arranged in a manner such that when thepiston is located in the region of itsthrottle-closng position thethrottle is operable manually by said power control member, a springadapted to move said piston to its throttle-closing positionv whenoperating fluid is relieved from said piston, and a valve operableexteriorly of the power control mechanism for cutting off the flow ofoperating fluid to said piston and whereby transfer from automatic tomanual control of the throttle may be had at the will of a pilot oroperator.

l2. In power control mechanism for an internal combustion-engine havinga throttle-controlled inductionpassage, power means for operating thethrottle, variable datum means including a device responsive to changesin manifold pressure, an operating connection between said variabledatum means and said power means for automatically operating the latter,manual means for setting the datum of said device, means whereby whenthe power means is :ie-energized the throttle is moved toward closedposition andy a direct mechanical connection is established be tweensaid manual means and the throttle, and means operable at the-will of apilot or operatorl for de-energizing said power means.

13. For use with an engine having an intake manifold and an engine speedgovernor. control mechanism including variable datum means formaintaining a selected manifold pressure, a manually operable powercontrol member, means providing an operating connection between saidpower control member and said variable datum means and also betweensaidflatter member and said governor including a datum cam and an enginespeed cam and hydraulic motor means to which hydraulic flow iscontrolled by servo valves in turn controlled by said cams and wherebysaid power control member may be adjusted to obtain a selected manifoldpressure and coordinated engine speed, and means automatically becomingeffective at a given power setting of said power control member and inresponse to movement of said member to such given setting for varying'the datum and speed settings from the values normally obtained by saidcams.

14. For use with an engine provided with an intake manifold and anengine speed governor and an element for adjusting the setting of saidgovernor, controlrme'chanism comprising variable

